Mystique Network Upgrade Successfully Activated

On February 12, 2022, at block 14,525,000, the Ethereum Classic network successfully activated the Mystique network upgrade. The upgrade brought selected improvements from Ethereum's London release to ETC while deliberately omitting EIP-1559's fee-burning mechanism.

## What Was Included

Mystique implemented four EIPs from Ethereum's London upgrade:

- **EIP-3529 — Reduced Refunds**: Removed gas refunds for SELFDESTRUCT and reduced SSTORE refunds. This eliminated gas token exploits that were distorting block gas usage.
- **EIP-3541 — Reject 0xEF Bytecode**: Prevents deployment of contracts starting with the 0xEF byte, reserving the prefix for future EVM Object Format (EOF) standards.
- **EIP-3198 — BASEFEE Opcode**: Makes the base fee accessible to smart contracts via a new opcode.
- **EIP-3855 — PUSH0 Instruction**: Adds a zero-cost PUSH instruction for pushing the value 0 onto the stack, reducing gas costs for common operations.

## What Was Omitted

### EIP-1559 Base Fee Burning
The most notable omission was EIP-1559's fee-burning mechanism. ETC chose not to implement the automatic burning of base fees because:

- ETC has a **fixed supply cap** under ECIP-1017. Burning fees would reduce the effective supply below the intended ~210.7M cap.
- The Olympia proposal (later formalized in ECIP-1109) would redirect the base fee to a community treasury instead of burning it.

## ECIP Reference

Mystique was specified in **ECIP-1104**.

## Activation

The upgrade activated smoothly across all ETC clients. No chain splits or network disruptions were observed. Miners and node operators had upgraded their software in advance following the successful Mordor testnet activation.

## Significance

Mystique demonstrated ETC's approach to protocol upgrades: adopt proven EVM improvements for compatibility while making independent decisions about economic mechanisms. The deliberate omission of EIP-1559 burning showed that ETC evaluates each change against its own principles rather than automatically following Ethereum.